The major change, since the previous posting, are serveral new
trusted-key options (migratable, pcrlock, keyhandle, keyauth, blobauth),
described below, based on suggestions by Jason Gunthorpe. By default,
trusted keys work as previously described.
Trusted and Encrypted Keys are two new key types added to the
existing kernel key ring service. Both of these new types are
variable length symmetic keys, and in both cases all keys are
created in the kernel, and user space sees, stores, and loads
only encrypted blobs. Trusted Keys require the availability of a
Trusted Platform Module (TPM) chip for greater security, while
Encrypted Keys can be used on any system. All user level blobs,
are displayed and loaded in hex ascii for convenience, and
are integrity verified.
Trusted Keys use a TPM both to generate and to seal the keys.
Keys are sealed under a 2048 bit RSA key in the TPM, and optionally
sealed to specified PCR (integrity measurement) values, and only
unsealed by the TPM, if PCRs and blob integrity verifications match.
A loaded Trusted Key can be updated with new (future) PCR values,
so keys are easily migrated to new pcr values, such as when the
kernel and initramfs are updated. The same key can have many
saved blobs under different PCR values, so multiple boots are
easily supported.
By default, trusted keys are sealed under the SRK, which has the
default authorization value (20 zeros). This can be set at
takeownership time with the trouser's utility:
"tpm_takeownership -u -z".
Usage:
keyctl add trusted name "new keylen [options]" ring
keyctl add trusted name "load hex_blob [pcrlock=pcrnum]" ring
keyctl update key "update [options]"
keyctl print keyid
options:
keyhandle= ascii hex value of sealing key default 0x40000000 (SRK)
keyauth= ascii hex auth for sealing key default 0x00... (40 ascii
zeros)
blobauth= ascii hex auth for sealed data default 0x00... (40 ascii
zeros)
pcrinfo= ascii hex of PCR_INFO or PCR_INFO_LONG (no default)
pcrlock= pcr number to be extended to "lock" blob
migratable= 0|1 indicating permission to reseal to new PCR values,
default 1 (resealing allowed)
The key length for new keys are always in bytes. Trusted Keys can
be 32 - 128 bytes (256 - 1024 bits), the upper limit is to fit within
the 2048 bit SRK (RSA) keylength, with all necessary structure/padding.
Encrypted keys do not depend on a TPM, and are faster, as they
use AES for encryption/decryption. New keys are created from kernel
generated random numbers, and are encrypted/decrypted using a
specified 'master' key. The 'master' key can either be a trusted-key
or user-key type. The main disadvantage of encrypted keys is that if
they are not rooted in a trusted key, they are only as secure as the
user key encrypting them. The master user key should therefore
be loaded in as secure a way as possible, preferably early in
boot.
Usage:
keyctl add encrypted name "new master-key-name keylen" ring
keyctl add encrypted name "load master-key-name keylen hex_blob" ring
keyctl update keyid "update master-key-name"
The initial consumer of trusted keys is EVM, which at boot time
needs a high quality symmetric key for HMAC protection of file
metadata. The use of a trusted key provides strong guarantees
that the EVM key has not been compromised by a user level problem,
and when sealed to specific boot PCR values, protects against
boot and offline attacks. Other uses for trusted and encrypted
keys, such as for disk and file encryption are anticipated.
Mimi Zohar
Dave Safford
Mimi Zohar (4):
lib: hex2bin converts ascii hexadecimal string to binary
key: add tpm_send command
keys: add new trusted key-type
keys: add new key-type encrypted
drivers/char/tpm/tpm.c | 17 +
include/keys/encrypted-type.h | 30 +
include/keys/trusted-type.h | 32 ++
include/linux/kernel.h | 1 +
include/linux/tpm.h | 3 +
lib/hexdump.c | 16 +
security/Kconfig | 31 +
security/keys/Makefile | 2 +
security/keys/encrypted_defined.c | 816 +++++++++++++++++++++++++++
security/keys/encrypted_defined.h | 52 ++
security/keys/trusted_defined.c | 1096
+++++++++++++++++++++++++++++++++++++
security/keys/trusted_defined.h | 147 +++++
12 files changed, 2243 insertions(+), 0 deletions(-)
create mode 100644 include/keys/encrypted-type.h
create mode 100644 include/keys/trusted-type.h
create mode 100644 security/keys/encrypted_defined.c
create mode 100644 security/keys/encrypted_defined.h
create mode 100644 security/keys/trusted_defined.c
create mode 100644 security/keys/trusted_defined.h
--
1.7.2.2